The cells that were corroded didn't corrode on their own. They used the wrong bussbar. The packs were assembled using steel bussbar that rusted, and the corrosion caused a snowball effect and rusted the other cells. Once it started rusting, it spread to the cells quickly. The guy also lived near the ocean, where the salinity of the humid air is fairly high. Salt is a Catalyst.
I have 200 cells, and not 1 of them is corroded. They're in my garage in Portland, OR where the humidity is high.
Just don't use anything except for copper or tin plated copper to assemble.